Some storage benchmarks after applying a BIOS/UEFI firmware update to Astaroth (which uses an AMD Ryzen processor), adding Spectre mitigations. The benchmark results are surprising, with both benchmark results being markedly better. Old result first, new result second:

PS C:\WINDOWS\system32> Get-SpeculationControlSettings
Speculation control settings for CVE-2017-5715 [branch target injection]
For more information about the output below, please refer to support.microsoft.com/en-in/help/4074629
AMD CPU detected: mitigations for branch target injection on AMD CPUs have additional registry settings for this mitigation, please refer to FAQ #15 at portal.msrc.microsoft.com/en-us/security-guidance/advisory/…

Hardware support for branch target injection mitigation is present: True

I wonder if this performance improvement is due to the SSD having had its firmware updated?

Of note was that while CrystalDiskMark was found to be CPU-bound, Anvil's Storage Utilities was not.

In any case... Spectre patches have no meaningful impact on the storage performance of AMD Ryzen systems.